What is the basis for comparing a diamond's other proportions?

• A. Average girdle diameter.
• B. Table percentage.
• C. Total depth percentage.
• D. Girdle height.

Answer: (A)

Proportions are expressed relative to the girdle diameter, and the average girdle diameter provides the single reference width for the stone. Using the average girdle diameter as the baseline lets you compare other measurements consistently—table width, total depth, crown height, and pavilion depth are all calculated as percentages of that baseline. Averaging across the girdle also minimizes the effect of any slight irregularities around the edge, giving a stable standard for comparison. The other options are specific proportions or separate dimensions themselves (table width as a percentage, depth as a percentage, or girdle height as its own measurement) and aren’t the universal reference used to scale the rest of the proportions.